TiAl-base alloys exhibit outstanding balanced mechanical properties at high temperatures, which are considered as important light-weight structural candidates within 650-1000℃ in aerospace industry. The microstructures of TiAl alloys are unstable and decompose at evaluated temperatures, which would affect the mechanical properties. Therefore, the thermal stability and the microstructural evolution and the influence on properties have attracted close attentions for a long time. In this paper, the connotation of thermal stability of TiAl-base alloys is introduced. The microstructures evolution and phase transition of TiAl-base alloys under high temperature conditions are discussed and analyzed, including the discontinuous coarsening of α2/γ lamella and the continuous coarsening of γ lath strip, the decomposition of α2 phase and the change of B2 (ω) phase. The effects of temperature, time, alloying elements and thermal load on microstructures, thermal stability and mechanical properties of TiAl alloy are summarized and summarized. Finally, the research direction of thermal stability of TiAl alloy is summarized and forecasted.